Many beachgoers are captivated by the beautiful, coin-shaped objects that wash ashore, often prompting curiosity about whether these intriguing finds are alive. While commonly collected as souvenirs, the pristine white disks are not living organisms. Understanding the differences between a living sand dollar and its skeletal remains helps in appreciating these marine creatures and practicing responsible beach etiquette.
Understanding the Sand Dollar
Sand dollars are living marine animals, specifically a type of flattened sea urchin belonging to the class Echinoidea. They are part of the larger group known as echinoderms, which also includes sea stars and sea cucumbers. These invertebrates typically inhabit sandy seafloors in coastal waters, often found just beneath the surface of the sand.
Sand dollars play a role in marine ecosystems by feeding on small organic particles, algae, and microscopic organisms found along the ocean floor. They use thousands of tiny spines and hair-like cilia covering their bodies to move across the seabed and to burrow into the sand. This unique adaptation allows them to navigate their environment and capture food efficiently.
Identifying a Live Sand Dollar
A living sand dollar appears distinctly different from the white, smooth objects commonly found on beaches. Live sand dollars are typically covered in a velvety layer of tiny, movable spines. These spines give them a soft, fuzzy appearance and are responsible for their movement and ability to burrow.
The color of a live sand dollar varies, often appearing in shades of brown, gray, purple, or reddish-brown, depending on the species. If gently handled, a live sand dollar’s spines may show slight movement, indicating it is alive. Some live specimens might also release a harmless yellowish substance called echinochrome, which can temporarily stain the skin. Live sand dollars are usually found partially or fully buried in the sand in shallow coastal waters and cannot survive for long periods out of water. If you encounter a live sand dollar, it should be gently returned to its natural habitat to ensure its survival.
The Transformation of a Dead Sand Dollar
The familiar white, disk-shaped objects found scattered on beaches are not living sand dollars but rather their calcified skeletons, known as “tests.” After a sand dollar dies, its soft tissues decompose, leaving behind this hard, brittle structure made of calcium carbonate. The spines, which covered the living animal, fall off during this process.
Exposure to sunlight and the ocean’s currents then bleaches these tests, turning them pure white and smoothing their surface. This natural process removes any remaining organic material and the vibrant colors seen in live specimens. These smooth, white tests, often featuring a distinctive five-pointed petal pattern, are what beachcombers typically find and collect. The appearance of these bleached skeletons is what gives the sand dollar its name, resembling an old coin.